1. Field of the Invention
The present invention relates to a microwave mode transducer for changing the rectangular TE.sub.10 mode into the circular or semi-circular TE.sub.01 mode and vice versa, particularly in the frequency range extending from a few GHz to more than 100 GHz.
2. Description of the Prior Art
In this type or transducer energy propagating in the rectangular TE.sub.10 mode is transformed into circular TE.sub.01 mode for example, to be transmitted over a distance by a large diameter circular guide e.g. 50 to 70 mm, or a helical or other guide, having very low losses in the circular TE.sub.01 mode and therefore not greatly attenuating the energy transmitted. This transmission mode is used particularly for distances greater than 100 meters. A reverse transducer, i.e. from the circular TE.sub.01 mode to the rectangular TE.sub.10 mode is used at the other end of the connection by circular or other guide connection. Such transducers for changing from the rectangular TE.sub.10 mode to the semi-circular or circular TE.sub.01 mode, can be used in semi-circular wave guide diplexers employed in a multiplexed communications connection formed by circular wave guides; these diplexers are, for example, similar to those described in French Pat. No. 2,246,089, in the Applicant's name. These transducers can be used for extracting the frequency sub-bands of a semi-circular diplexer and/or as measurement couplers for semi-circular wave guide structures and/or, even, as couplers between rectangular guides and circular guides.
Such transducers also enable transmitters to be connected to aerials in microwave stations, the rectangular TE.sub.10 mode often being used.
Several transducers of this type are known:
The "Marie" type transducer in which electromagnetic fields are transformed into the rectangular TE.sub.20 mode and into the rectangular TE.sub.22 mode and lastly into the circular TE.sub.01 mode. The "Marie" transducer described particularly in the article "A new TE.sub.10 - TE.sub.01.sup.0 mode transducer mm -- waves", published on p. 73-75, "Microwave Journal" of February, 1970, has a complex structure and large dimensions which it is difficult to determine precisely.
A transducer having a variable interior cross-section; an originally rectangular cross-section is transformed to obtain a transducer having an intermediate triangular then a semi-circular, then circular cross-section. They are difficult to produce and must be equipped with spurious mode filters, spurious modes occurring at the transducers.
Another transducer of this type can be constituted by a semi-circular guide coupled to a cylindrical or rectangular resonant cavity. In this transducer coupling is effected by a single orifice and the semi-cylindrical guide is closed by a short-circuit which concentrates energy at a coupling orifice. This transducer operates like a selective band-pass filter.
Preferred embodiments of the present invention avoid these disadvantages.